Territorial Behavior by Conifers Using Allelochemicals
Allegheny College Department of Biology and Environmental ScienceBy: Albrando Lorenzo Lucino Jr, B.S, B.A
IntroductionPlants, just like animals, are territorial and are able to control the size of their populations to secure resources from potential interspecific competitors. This particular mechanism that plants use as a form of territorial defense is called Allelopathy. Allelopathy refers to the chemical inhibition of one species by another. The "inhibitory" chemical is released into the environment where it affects the development and growth of neighboring plants. Allelopathic chemicals can be present in any part of the plant.
They can be found in leaves, flowers, roots, fruits, or stems. They can also be found in the surrounding soil. Target species are affected by these toxins in many different ways. The toxic chemicals may inhibit shoot/root growth, they may inhibit nutrient uptake, or they may attack a naturally occurring symbiotic relationship thereby destroying the plant's usable source of a nutrient.
We have to take into consideration the hypotheses of the past experiments in the study of hemlocks (Tsuga canadensis) in Bousson Forest. These past two hypotheses were that the hemlock canopy is sufficiently tight that little light penetrates to the forest floor, and the herbaceous/sapling layer is light limited. The second is that the hemlocks are releasing Allelopathic compounds that inhibit the germination or growth of potential competitors under their canopies.
In this particular experiment, we will be examining the potential for Allelopathic effects of hemlock (Tsuga canadensis) on the germination and early growth of ryegrass (Lolium) and pea (Pisum). In this given experiment, we will be testing the following 6 hypotheses that water soluble compounds leached from (1)fresh hemlock foliage,(2) hemlock liter, and (3) hemlock soil exert a significant inhibitory effect on the germination of rye. Water soluble compounds leached from (4) fresh hemlock foliage, (5) hemlock litter, and (6) hemlock soil exert a significant inhibitory effect on the rate of the radicle growth in peas.
Methods We filled the bottom of 10 plastic culture dishes with potting soil and 10 more with fresh hemlock foliage, 10 more with hemlock litter and 10 more with soil from dense hemlock canopy. We then placed 25 rye seeds on the surface of the soil, foliage or litter in each of the 40 culture dishes. Maintained a constant water schedule to initiate germination and place the covers on top of the culture dishes and place it in proper storage.
We then filled the bottom half of 10 plastic culture dishes with potting soil (the control treatment), 10 more with hemlock litter, 10 more with fresh hemlock foliage, and 10 more with soil excavated under dense hemlock canopy. Placed 10 pea seeds in each of the 40 culture dishes; maintained a constant water schedule and checked up on seeds daily for the next week. After a week, we then measured the length of the roots to shoots in centimeters for all the peas and rye seeds and recorded them. We then made an ANOVA analysis for both the Germination/25 and to find out the Radicle length. We also proceeded to complete a chi squared test.
Data
Figure 1 and Figure 4 is titled "ANOVA Table for (either Germination/25, or Radicle length)", and it gives the details of the ANOVA analysis. The details are not important except to indicate that we had 4 treatments (potting soil, hemlock soil, hemlock litter, and hemlock foliage) and 87 observations for germination, and 306 measured radicles among those 4 treatments. If the P-Value is <0.05 we can say that at least one significant difference exists among the four treatments; also gives some statistics of the individual treatments: count (number of observations), mean, std. deviation (a measure of variability) and standard error (another measure of variability but adjusted for sample size).Figure 2 and 5 are histograms of the data. The treatments are identified on the X axis and the mean of each treatment is given on the Y axis. The error bars represent +/- 1 std. error. Histograms on figures 2 and 5 are different in that hemlock foliage had more cell means than hemlock litter, hemlock soil and potting soil (going in decreasing order); whereas the histogram in Figure 5 shows more cell mean on the hemlock soil, hemlock litter, potting soil and hemlock foliage (going in increasing order). Figures 3 and 6 are comparisons between every possible pair wise combination of treatments. If an "S" appears to the right of the comparison there is a significant difference between the compared treatments. Figure 3 shows there is no significant difference between hemlock litter and hemlock soil, hemlock litter and potting soil, hemlock soil and potting soil. There is a significant difference between the compared treatments of hemlock foliage and hemlock litter, hemlock foliage and hemlock soil, hemlock foliage and potting soil. Whereas Figure 6 shows that There is no significant difference between hemlock litter and hemlock soil, hemlock litter and potting soil. There is a significant difference between the compared treatments of hemlock foliage and hemlock litter, hemlock foliage and hemlock soil, hemlock foliage and potting soil, hemlock soil and potting soil.
DiscussionFrom looking at the results section, we notice that there are allelopathic incidents taking place within the experiments. The theses statements that stated that soluble compounds leached from fresh hemlock foliage, hemlock litter and hemlock soil exert a significant inhibitory effect on the germination of rye is not supported because from looking at the data from Figure 2, we observe that there indeed was growth in cell mean in the ryes that were placed in hemlock litter, hemlock litter, and hemlock soil as compared to the controlled experiment. There was an observable growth, rather than inhibition of germination.
The other three hypotheses that stated water soluble compounds leached from fresh hemlock foliage, hemlock litter and hemlock soil exerts a significant inhibitory effect on the rate of radicle growth in peas showed mixed results. The 4th hypothesis that stated that fresh hemlock foliage exerts a significant inhibitory effect on the rate of radicle growth in peas was supported since the cell mean rate in radicle growth was miniscule as compared to the controlled experiment. The 5th hypothesis that stated hemlock litter exerts a significant inhibitory effect on the rate of radicle growth in peas was not supported because there was a high cell mean in radicle growth, as it was higher than the controlled experiment. The 6th hypothesis that stated hemlock soil exerts a significant inhibitory effect on the rate of radicle growth in peas was not supported since Figure 5 indicates a high cell mean growth as compared to the controlled experiment.
*Published in the Allegheny College Science Journal*
*Federal Grant Money was used in this research*Linkback:
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